Vacuum tube keying circuit



Sept. 9, 1952 J. c. SEDDON 4 2,610,294

I VACUUM TUBE KEYING CIRCUIT Filed June 15, 1945 INPUT NEGATIVE KEYING VOLTAGE J. CARL SEDDON Patented Sept. 9, 1952 UNITED STATES ?TENT OFFICE VACUUM TUBEKEYING CIRCUIT John Carl'seddon, Washington, n. 0. Application June 13, 1945, Serial No. 599,291

5 Claims. (o1. zoo-av) (Granted under the act of March 3, 1883, as

amended April'30, 1928; 3-70 0. G.- 757) This invention relatesto the keying of vacuum tube circuits, and is particularly directed to a means by which vacuum tube vuiparatus may be keyed, orrnodulated with rectangular impulses, recurrently at a wide range of speeds.

An object of this invention is to provide a means by which a vacuum tube can be alternately rendered operative and blocked by effecting variations in its grid bias potential.

Another object of this invention is to provide a means for keying :a vacuum tube-at speeds up to several hundred thousand impulses per sec-nd. Another'object of this invention is to provide a means whereby a vacuum tube oscillator can be keyed by effecting variations in the grid bias potential of the'oscillator tube.

A further object of this invention is to provide a means whereby the output of a vacuum tube oscillator can be modulated with rectangular impulses at speeds up to several hundred thousand impulses per second. I

Still a further object of this invention is to pr vide a means of yin -a high-p w r va tube oscillator or transmitter with small apparatus consuming little power.

Still another object of this invention is to provide a means for keying a high-power vacuum oscillator or transmitter at high or low speed without the necessity for mechanically breaking high-voltage or heavy-current circuits.

The invention will be described with reference to the drawing append-ed hereto, which is a schematic diagram. of an exemplary embodiment of the invention. f

In the drawing. the vacuum tube circuit to be keyed is shown as a Hartley oscillator incorporating tube 2o. Inductance 25 and condenser 24 are connected in parallel to form a tank circuit. One side of the tank circuit is connected to plate 23 of tube 20, the'other side being connected through condenser 3'0 to grid 22 of tube 2!). Cathode 2i of tube 20 and the negative side of D. C. source 28 :aregrounded. Tap 3| on inductance 25 is connected to the positive side of D. C. source 28 andv is by-passed to ground by condenser 25: v

Grid 22 of oscillator tube 20 is. connected to cathode ll of tube Ill through resistor I9. In parallel with resistor I9 is the network comprising condenser 9, radio-irequency choke coil ll,

and resistor l8 in series. Plate IB of diode tube M is connected to thejuncti-on of condenser 9 and choke coil l1. Cathode P of diode tube [4 and cathode ll of tube Iii are connected together. Cathode ll of tube It is connected to the plate 6 2 of tube 2 through radio-frequency choke coil 7 and resistor .3 in series. Control grid 13 of tube i0 is connected directly toplate 6 of tube 2. Screen grid I Z and plate 32 of tube it areg-rounded. The positive side of 'D. C. source 2'! is grounded, and the negative side of D. C. source 2? is connected to cathode 3 of tube 2. Screen grid 5 of tube 2 is connected to ground through resistor 2%. Control grid 4 is connected to cathode 3 of tube 2 through resistor l.

Keying impulses from an external source are applied between control grid 4 and cathode 3 of tube 2, and are so polarized that during an impulse grid 4 is negative relative to cathode 3.. These keying impulses need be only of sufficient magnitude to cause plate current cut-off in tube 2. In a practical construction using type 807 tubes as tubes 2 and lo, volts was found to be adequate amplitude for the keying impulses.

The system operates as follows. The D.-C. grid return circuit for oscillator tube 20' comprises resistor l9 and tube It) in series; hence the grid bias on oscillator tube 20 is the sum of the 'D.-C. voltage drops across resistor l9 an-dtube Ill. Tube Ill, resistor 8, choke coil 1, and tube 2 are in series across D.-C. source 21 and current from that source normally flows through them. When no voltage from an external source is applied between the control grid and cathode of tube 2, tube 2 presents a low impedance, since its grid and cathode are at the same'potential. Tube it is a high impedance under the same conditions because its is negative relative to its cathode by the amount of the voltage drop across resistor 8 and choke coil 1. Normally, therefore, most of the voltage from D.-C. source 21 is developed across tube It. As a result, the grid of oscillator tube 20 is biased so far negative that the tube is completely blocked and unable to start or maintain oscillations.

When a keying voltage is applied between the grid and cathode of tube 2', tube 2 ceases to pass current. This causes the voltage drop across resistor 8 to disappear, and the collapsing magnetic field of coil 1 produces a positive surge of voltage which very quickly drives the control grid of tube [0 to a positive value. Tube 10 becomes a low impedanoaand the cathode of tube it rises toward ground potential, thus removing all the D.C. bias from the grid of oscillator tube 20 and allowing oscillations to start. After oscillations have started in tube 20, a grid leak voltage is built up across resistor l9 and tube It,- in conventional fashion. long as keying voltage is applied to tube 2, tube It) remains a low impedance, since its grid is at or above the potential of its cathode so long as tube 2 is cut off. As tube oscillates condenser 9 is charged from condenser with the side of condenser 9 connected to grid 22 going negative to a voltage equal to the grid leak potential developed across resistor [9. The function of coil l1 and resistor 18 is to prevent an excessive peak value of oscillator grid current by making this charging process gradual.

When the keying voltage is removed from the grid of tube 2, tube 2 becomes again a low imposed to accumulate a charge proportional to the flow of grid leak current during operation of the electron tube; impedance means operative to limit the rate of flow of grid leak current into the con denser; and unilateral impedance means operative to effect rapid discharge of thecondenser after blocking of the tube; the charge on the condenser accumulated during electron tube operation being efiective on termination of the positive voltage shifts as additional blocking bias for the electron tube.

pedance. It starts a draw current. The plate po tential of tube 2 and the control grid potential of tub-e [0 drop very sharply. Tube l0 becomes again a very high impedance, and grid 22 of oscillator tube 20 is suddenly biased very negatively, the instantaneous negative bias being equal to the voltage across tube Ill plus all the voltage across condenser 9. This sudden surge of neg-ative bias completely blocks tube 26 and stops oscillations therein. Condenser 9 quickly discharges through diode l4 and resistor l9.

Oscillations build up very rapidly after the application of a keying impulse; the oscillations reach 90% of final amplitude within a fraction of a microsecond after keying voltage is applied.

Recovery time after a keying impulse has ended is likewise very rapid; in a practical construction embodying this invention it was found to be less than one microsecond.

These properties of the invention make possible its use at extremely high keying speeds; the practical construction already mentioned could be successfully keyed at a speed of about three hundred thousand impulses per second. The system may likewise be used at as slow speed as desired, since both on and off conditions are stable.

It will be understood that the embodiment of the invention herein described is exemplary only, and that the scope of the invention is to be determined from the appended claims.

The invention describedherein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. In combination, a vacuum tube having control grid means, a source of supply voltage connected to said vacuum tube, a negative blocking voltage connected to said grid means, said negative blocking voltage including means operative intermittently to apply a positive voltage shift to the grid means and effect grid current conduction; a grid leak return circuit including a condenser connected between the negative blocking voltage and the grid means, said condenser disposed to accumulate a charge proportional to the flow of grid leak current during operation of the vacuum tube; and impedance means operative to limit the rate of fiow of grid leak current into the condenser; the charge on the condenser accumulated during the vacuum tube operation being effective ontermination of the positive voltage shift as additional blocking bias for the vacuum tube.

2. In combination, an electron tube having control grid means, a source of supply voltage connected to said vacuum tube, a negative blockin voltage connected to said grid means, said negative blocking voltage including means operative intermittently to apply a positive voltage shift to the grid means and effect grid current conduction; a grid leak return circuit including a condenser connected between the negative blocking Noltage and the grid means, said condenser dis- 3. In combination, a first electron tube having control grid means; a source of supply voltage connected to saidvacuum tube, a second electron tube having a space-current path; a grid leak return circuit for the first tube comprising the space-current path of the second tube; means charge proportional to the fiow of grid leak cur-.

rent during operation of the first tube; impedance means operative to limit the rate of flow of grid leak current into the condenser; and unilateral impedance means operative to effect rapid discharge of the condenser after blocking of the first tube; the charge on the condenser accumulated during operation of the first tubebeing effective as additional blocking bias if'or the first tube when the potential across the second tube is shifted in a negative direction.

4. In combination, an electron tube having a cathode and a control electrode, a vacuum tube having cathode and anode electrodes and a space current path fed thereby, a grid return. circuit for the first tube comprising a direct current resistance element and the space current path of said vacuum tube connected in series between the grid and cathode electrodes of said electron tube, said resistance element serving to connect the cathode electrode of said vacuum tube to the grid electrode of said first tube, an electron discharge device-and asource of direct current potential connected in series with the anode cathode path of said vacuum tube to bias the cathode of said vacuum tube negative of the anode thereof, and means operative to vary the impedance of said discharge device and thereby the voltage at the cathode of said vacuum tube.

5. In combination, an electron tube having a cathode and a control electrode, a second electron tube having cathode and anode electrodes and a space current path fed thereby, a grid return circuit for the first tube comprising'a, direct current resistance element and the space current path of said second tube connected in series between the rid and cathode electrodes of said electron tube, said resistance element serving to connect the cathode of said second tube to the control electrode of the first tube, an energy storage element connected in parallel relation with said resistance element, an electron discharge device and a source of direct current potential connected in series with the anode cathode path of said second electron tube, to bias the cathode of said second tube negative of anode thereof, and means operative to vary the imped- 5 ance of said discharge device and thereby the Number voltage at the cathode 0f said second electron 1,984,105 tube. 2,027,038 2,060,988 J. CARL SEDDON. 5 2307 ,571 1 2,329,137 REFERENCES CITED 2,409,577 The following references are of record in the 2, 5 file of this patent:

. 10 UNITED STATES PATENTS P 32 2 Number Name Date 1,683,012 Appleby Sept. 4, 1928 1,849,865 Davis Mar. 15, 1932 1,868,034 Urtel 1 July 19, 1932 15 6 v Name Date etzmann Dec. 11, 1934 ansell Jan. 7, 1936 Hansen Nov. 17, 1936 Andrews July 9, 1940 Richards Sept. 7, 1943 Mat-son Oct. 15, 1946 Owen Dec. 14, 1948 FOREIGN PATENTS Country Date Germany Nov. 13, 1929 Germany Dec. 20, 1930 

